Comments on: Climate inertiahttps://ourchangingclimate.wordpress.com/2016/08/09/climate-inertia/
Bart Verheggen's weblog on climate change issuesThu, 01 Feb 2018 19:03:12 +0000hourly1http://wordpress.com/By: Singingwayhttps://ourchangingclimate.wordpress.com/2016/08/09/climate-inertia/#comment-34755
Wed, 17 Aug 2016 04:07:38 +0000http://ourchangingclimate.wordpress.com/?p=3046#comment-34755“Those who caused the problem are in the best position to solve it, but since the full consequences will not materialize until much later, they have the least incentive to do so.” To me, this is the answer as to why oil company CEOs can sleep at night. Can look at their grandchildren and smile with smug complacency. This is the problem — human lifespans are so short compared to the earth systems we are impacting. The only people trained to think in terms of milleniums are climate scientists, paleontologists, archaeologists, and astronomers.
]]>By: Paul Price (@swimsure)https://ourchangingclimate.wordpress.com/2016/08/09/climate-inertia/#comment-34745
Sun, 14 Aug 2016 09:13:34 +0000http://ourchangingclimate.wordpress.com/?p=3046#comment-34745@Bob

Good to see we are getting closer to some agreement if not completely!

Of course, the case of an immediate and total cessation of CO2 emissions is hypothetical but that is the point of M&S article, to separate the natural from the human system. Investigating such thought experiments is an essential part of science.

You say the M&S paper “uses a rather unusual definition of ‘committed warming’ which differs from IPCC AR4 and AR5′. But the reference you give from AR4 and AR5 both provide a set of alternative definitions of climate change commitment, one of which is the ‘zero emission commitment’ considered by M&S.

IPCC AR5 WG1 Ch.12 p.1106, FAQ 12.3, says:

“Stopping emissions today is a scenario that is not plausible, but it is one of several idealized cases that provide insight into the response of the climate system and carbon cycle.”

And the points M&S make are also made on the next page of the FAQ:

“Eliminating CO2 emissions only would lead to near constant temperature for many centuries. Eliminating short-lived negative forcings from sulphate aerosols at the same time (e.g., by air pollution reduction measures) would cause a temporary warming of a few tenths of a degree, as shown in blue in FAQ 12.3, Figure 1. Setting all emissions to zero would therefore, after a short warming, lead to a near stabilization of the climate for multiple centuries. This is called the commitment from past emissions (or zero future emission commitment). The concentration of GHG would decrease and hence the radiative forcing as well, but the inertia of the climate system would delay the temperature response.”

Therefore, it is not ‘arbitrary’ or unrealistic to claim that the natural system has ~ zero net physical inertia, it is the consensus scientific understanding.

As you say, the reality of our situation is that living within and changing that natural system is human society, which continues to change the surface energy balance by the accumulation on CO2 in the atmosphere due to burning fossil fuels.

Of course it is correct that future human emissions will add to the present level of warming. Even peaking emissions now and getting to zero emissions at some point could easily add as much CO2 to the atmosphere as released in all of past human history, thereby adding to warming. But this is human-caused inertia due to past, present and future choices.

To be sure humanity is part of the physical system but we are the agency that has caused and is causing the current rapid global warming, so separating the inertia in the human system from that in the remainder of the physical system seems entirely justifiable and helpful to the analysis.

(Apart from CO2, cutting aerosol emissions would give more warming, but that could be cancelled out by cutting methane emissions causing cooling.)

As IPCC and M&S point out, the zero emissions scenario provides important guidance for policy: there is no CO2 warming in the pipeline from the physical system; sustaining annual cuts in human-caused global emissions will reduce future warming starting immediately; and, limiting climate change is possible if emissions go to net zero, resulting essentially immediately in no future CO2 warming from that point.

Our collective choices determine whether we accept a path to climate stabilisation at the lower end of the range now possible due to our future emissions – a higher average temperature level that will still be very changed from the Holocene climate. Otherwise, in the absence of substantial near-term cuts in emissions, we will continue on the current path to far more dangerous levels of warming.

All the more so, because in reality we have to deal with a very different situation where CO2-emissions will not cease instantly and totally — and then there exists unavoidably a net physical climate inertia which is not cancelled out…

The Matthews & Solomon paper uses a rather unusual definition of ‘committed warming’ which differs from IPCC AR4 and AR5, where it is considered to be: “The multi-model average warming for all radiative forcing agents held constant at year 2000 …”:

This is also what I said: “Mind you, this is IF current forcings (concentrations of CO2 etc. as well as aerosols) would remain unchanged.”

Matthews & Solomon however consider a *very* hypothetical case with:

— an immediate, abrupt and total cessation of all CO2 emissions;
— while at the same time aerosol pollution would stay as before?

The lack of realism is not so much in the 100% reduction but that it would be instant, and at the same time the aerosol pollution would remain.

Note however that there would still exist physical inertia but in THIS particular, special case they claim that the “equal and opposing effects of physical climate inertia and carbon cycle inertia” would cancel out.

It seems arbitrary to me to base the contention: “the natural system has zero net inertia“, on that ONE very special case where supposedly these two forms of inertia would precisely cancel.

All the more so, because in reality we have to deal with a very different situation where CO2-emissions will not cease instantly and totally — and then there unavoidably a net physical climate inertia which is not cancelled out…

And I agree this is a good piece too (as always from BV). My comment and this bit of discussion is to try to tease out the human side of the inertia from the natural to add to the discussion.

If you look again at the article neither of the M&S quotes you give contradict what I have pointed to. Their first figure, ‘How the climate system responds’, very clearly shows their result that “Net system inertia ~ zero” because “Physical climate inertia (warming)” is balanced by “Carbon cycle inertia (cooling)”.

Under the figure, top of p.439, they say:

“The climate response to CO2 emissions is influenced by both physical climate and carbon cycle inertia, with the result that the net system inertia is close to zero. Therefore, future climate warming depends only on current and future CO2 emissions, and the rate of warming will respond immediately to CO2 emissions cuts.”

On p.439, Matthews & Solomon also say:

“The climate system physics implies that further increases in warming could in principle be stopped immediately, but human systems have longer time scales.”

Their point (unless you think I am somehow misreading it) is that the natural system has zero net inertia and the human system – including its political economy, infrastructure lock-in and overall rebound-effect behaviour – is where the inertial lies.

The notion that there will be additional future warming or “warming in the pipeline” if the atmospheric concentrations of carbon dioxide were to remain fixed at current levels (1) has been misinterpreted to mean that the rate of increase in Earth’s global temperature is inevitable, regardless of how much or how quickly emissions decrease (2–4).

In their paper they say:

There would indeed be unrealized warming associated with current CO2 concentrations, but only if they were held fixed at current levels (1).

This does not mean that there is “zero system inertia” or that there would not be “warming in the pipeline”.

Andy Skuce pointed out in a tweet that he agrees with the blogpost by Bart:

Aerosols and non-CO2 apart, the modelling based estimate that the net system inertia is zero is in the paper ‘Irreversible Does Not Mean Unavoidable’ by Matthews and Solomon (sorry, before posting I managed to edit out the reference in my comment).

1) the energy imbalance of +0.77 W/m^2 has some considerable uncertainties. Across the whole of the literature this is estimated at between +0.5 and +1.0 W/m^2.

2) I am using the +1.0 °C since pre-industrial as if this is *all* the temperature increase we can expect for 2/3rd of the ERF. This is probably an underestimate, since not all of the feedbacks have had time to come into full effect since the ERF started to rise rapidly.

3) Again, this is assuming the aerosol load would remain unchanged. If you try to estimate what is currently in the pipeline *and* will be realised in some future situation without this aerosol load, there is more than 1/3rd of current ERF still in the pipeline.

4) Some current research suggest that the 2.3 W/m^2 is an overestimate (Surface albedo change due to land use may be more like -0.5 W/m^2). This would mean a larger part of ERF is still in the pipeline.

… if all human-caused CO2 emissions were to (magically) stop then there is actually no inertia in the natural part of the climate system and little or no ‘warming in the pipeline’ from it.

At the current CO2-concentration, other GHG’s and the current aerosol-load there is an Effective Radiative Forcing (ERF) of about +2.3 W/m^2.

See IPCC AR5 Chapter 8 and:

At the same time the increasing Ocean Heat Content makes it possible to estimate the energy imbalance — how much of this 2.3 W/m^2 has NOT yet been compensated for by the increase in surface temperatures. Recent studies put the energy imbalance at about +0.77 W/m^2 (e.g. Cheng 2016).

Ergo: 2/3rd of ERF has been compensated for by an increase of surface temperature of about 1.0 °C since pre-industrial.

1/3rd of ERF (the 0.77 W/m^2) is still in the pipeline. Since 2/3rd of ERF corresponds to 1.0 °C it means that +0.5 °C is still in the pipeline.

Mind you, this is IF current forcings (concentrations of CO2 etc. as well as aerosols) would remain unchanged. Stopping emissions now would obviously also cancel the (negative) forcing by aerosols. It is true that an hypothetical stop of all emissions would mean that the CO2-concentration would (slowly) start to fall as well.

However, if you want to estimate the “warming in the pipeline” at the *current* net forcing… this would be in the vicinity of +0.5 °C.